Heretofore known pump unloading valve devices have been expensive in that they have embodied two or more valves and pistons of different diameters slidably mounted in corresponding bores. Moreover, these valves often chatter.
Accordingly, it is the general purpose of this invention to provide a small, inexpensive nonchattering pump unloading valve device that includes two cylindrical valve members having the same diameter so as to be slidably mounted in a common bore each being biased in the same direction by its own spring means and so connected by a lost-motion connection as to be simultaneously shiftable in one direction upon storage reservoir pressure acting on one valve member reaching a chosen cut-out pressure until the other valve member begins to open a communication whereupon this other valve member is subject to pump discharge pressure to cause it to be quickly shifted relative to the one valve member to a pump unloading position in which the pump discharge is returned to a sump. Thereafter, as reservoir pressure is reduced, both valve members are simultaneously shiftable in an opposite direction to cut off flow from the pump to the sump whereupon the pump is reloaded after which the spring means acting on the other valve member shifts it relative to the one valve member to its original position with respect thereto.